1. Technical Field of the Invention
The presently disclosed invention pertains generally to a protective cover for a portable safety instrument, and more specifically to a protective cover that enhances the audible and visible output from alarms on such a device.
2. Background of the Invention
Portable safety devices are often used and worn by individuals who work in extreme environments. Such safety devices may monitor for concentrations of gases that are toxic, combustible, or contain volatile organic compounds (VOCs), or for oxygen deficits. Once a threshold limit is reached, the portable devices may actuate a visible, audible or vibrational alarm to warn the individual of potential danger.
As an example, workers at oil fields, oil production sites and refineries are often exposed to hydrogen sulfide, H2S, a colorless gas that at low concentrations has the well-known odor similar to rotten eggs. At higher concentrations, H2S rapidly deadens the sense of smell (150 ppm), can cause immediate collapse and unconsciousness (750 ppm), and even lead to cardiac arrest and death (1000 ppm). Because of the poor sensory warning (e.g. lack of smell when at toxic levels), extreme toxicity, and pervasiveness of this hazard, workers are often required to wear a personal gas detector for H2S at all times while they are at a work site where there is exposure potential.
The usefulness of a portable safety device, however, depends on the user's recognition of and response to the warning signals from the detectors as well as the accuracy of such detectors. For example, the worker must be able to hear the audible signal even under the extreme and often very loud conditions of many work environments, such as the oil refineries mentioned above. Furthermore, in many environments, it may be difficult for the worker to observe a visible signal due to goggles or ventilation equipment, or simply because the type of work they perform impedes such an ability. Vibrational alarms may not be detected by a worker wearing extra protective clothing.
Failure of portable safety devices to provide an accurate audible, visible or vibrational alarm is often linked to infrequent bump testing and calibration. It is vital to worker safety that such instruments are maintained and calibrated properly. In use, however, the worker may not take the time to perform such testing if it requires undue additional time and/or difficult procedures.
One approach to provide enhanced signal output from a portable safety device would be to add external speakers or additional lights to amplify the audible and/or visible alarms. The difficulty with such a solution is the increased size and weight of the portable device that such added features bring, and the increased power requirement placed on the instrument's battery to support such additional features.
Unpowered sound conducting structures have been proposed in the prior art to enhance the sound directed to a portable device such as a phone. For example, U.S. Pat. Nos. 1,797,891 and 5,778,062 both teach a bowl shaped reflector that may be positioned over the microphone of a phone to enhance the sound quality of the user's voice as they speak into the phone. The reflector acts to dampen environmental sounds while amplifying the user's voice.
Similar ideas have been disclosed to enhance the sound emanating from a mobile phone's internal speakers. U.S. Pat. No. 8,086,285 describes a mobile phone having a sound reflector that may be extended outward from the case near the phone's speaker to enhance the quality of the sound produced. The sound reflector is shown, however, to increase the length of the mobile phone by an additional 50%. U.S. Pat. No. 8,180,075 teaches a mobile phone housing that forms part of a resonance pipe that enhances sound produced by the phone's internal speakers in the range of 400-500 hertz (Hz).
Sound reflectors have also been disclosed as safety devices. For example, U.S. Pat. No. 5,243,152 describes a baffle for a personal alarm that may redirect the sound from the alarm so that it can't be muffled, such as in the case that an attacker places a hand over the speaker on the device. U.S. Pat. No. 4,963,855 teaches a set of passageways that redirect and increase the sound from a fire alarm in the manner of a resonance tube.
Non-portable unpowered sound conducting structures have also been proposed in the prior art. For example, U.S. Pat. App. No. 2002/0009195 describes a mounting stand for a mobile phone that includes a sound conducting horn assembly to amplify sound from the phones internal speakers. U.S. Pat. No. 7,778,431 teaches a mounting stand for a mobile phone that enhances the sound generated by the phone's internal speakers through the use of a resonator shell that includes a cavity and a reflecting surface. The cavity has a volume of 100 to 200 cm3 and provides a resonant frequency response which is tunable to between 1500 and 500 Hz; the greater the size of the internal cavity the lower the frequency.
While each of the aforementioned patents and application provide methods to enhance the sound quality of a portable device, they all require additional apparatus that is comparable in size to the portable device itself. For example, the resonance shell disclosed in U.S. Pat. No. 7,778,431 comprises a cavity of 100 to 200 cm3. If such a cavity were added to a standard portable device, it would require the addition of between 1 to 3 inches of thickness to the device. Further, the sound reflector of U.S. Pat. No. 8,086,285 would add considerable length to a portable device and may not direct the sound toward an individual who is wearing the device, as is frequently the case for portable safety devices.
Smaller equipment is known, such as the resonance pipe of U.S. Pat. No. 8,180,075, that amplifies sound in the range of 400-500 Hz. However, that apparatus is directed to sound in the frequency range of the spoken voice (e.g. typically in the range of 80 to 1200 Hz). None of the prior art describes apparatus that is capable of amplifying sound at resonance frequencies that are commonly used for alarms (2000-4500 Hz). Further, the prior art does not describe sound amplification that is suitable for addition to a portable device that must be kept small and lightweight, nor does it describe methods for amplifying the signal from a visible alarm.
The prior art has disclosed sound redirecting elements such as the sound reflectors taught in U.S. Pat. Nos. 5,243,152 and 8,086,285, the sound tubes taught in U.S. Pat. Nos. 4,963,855 and 8,180,075 and U.S. Pat. App. 2002/0009195, and the sound chamber taught in U.S. Pat. No. 7,778,431. However, none of those patents describe redirecting sound pressure waves from an audible alarm in the resonance frequency range of 2000 to 4500 Hz. Nor do they describe redirecting sound pressure waves so as to enhance the wearer's detection of the audible signal in an environment of a high level of background noise.
There was also a need in the prior art to make functionality testing and calibration of improved portable gas monitors simple and fast. A correlation between bump test intervals and gas detector failures has been established (“Why bump testing saves lives,” D. Wagner, Industrial Scientific Corporation). An extension of the bump test interval from 1 day to 1 month was found to correlate to a 4 to 5 fold increase in the probability of device failure. This increase in failure rate obviates the advantages of a calibration gas chamber that is simple to attach and easy to use.
Accordingly, there was a need in the art for an unpowered apparatus to amplify the audible and visible alarms of a portable safety gas monitoring device. Further, there was a need in the art for a portable testing apparatus that makes bump testing and calibration of a portable safety device faster and more straightforward.